Method of and apparatus for making spiral heat exchangers



May 9, 1950 A. R. COLLINS ET AL 2,57,@94

METHOD OF AND APPARATUS FOR MAKING SPIRAL HEAT EXCHANGERS Filed Sept. 8,1944 6 Sheets-Sheet l May 9, 3950 A. R COLLINS ETAL METHOD OF ANDAPPARATUS FOR MAKING SPIRAL HEAT EXCHANGERS 6 Sheets-Sheet 2 Filed Sept.8, 1944 1 May 9 11956 A. R. COLLINS ETTAL 2,507fl9 METHOD OF ANDAPPARATUS FOR MAKING SPIRAL HEAT EXCHANGERS ,Filed Sept. 8, 1944 6Sheets-Sheet 5 May 9, 1950 A. R. COLLINS ErAL 2,507,094

METHOD OF AND APPARATUS FOR MAKING SPIRAL HEAT EXCHANGERS 6 Sheets-Sheet6 Filed Sept. 8, 1944 fatented May 9, 1956 METHOD or AND APPARATUS FORMAKiNG SPIRAL HEAT EXCHANGERS Arthur R. Collins, Park Ridge, John H.Leslie, 11, Winnetka, and Charles T. Novak, Oak Park, 111., assignors toStewart-Warner Corporation, Chicago, 111., a corporation of VirginiaApplication September 8, 1944, Serial No. 553,150

3 Claims.

The present invention pertains to heat exchangers and more particularlyto a method of constructing heat exchangers, apparatus for making heatexchangers, and the heat exchanger unit.

Considerable work has been done to provide improved heaters and heatexchangers for aircraft. One development is a novel type of heaterincluding an improved form of heat exchanger having heat transfersurfaces of large area operating efiiciently to transfer heat from thehot products of combustion to ventilating air. In this heat exchangerone of the fluids flows in a generally spiral path defined by spacedspirally arranged walls, while the other fluid preferably flowstransversely of the first fluid through the space between the externalsurfaces of said walls. The generally spiral path is the one followed bythe hot products of combustion which preferably enter the heat exchangeraxially and centrally thereof. The other fluid, i. e., the fluid flowingtransversely or axially, is the air to be heated.

In order to enhance the transfer of heat, the

spiral path, through which the hot products of combustion flow, isarranged so that the effective area of the path is gradually decreasedatleast through a considerable portion thereof, thereby to increase therate of heat transfer. It appears that the gradual constriction rtapering of the area and the spiral flow causes the hot products ofcombustion to impinge against the heat transfer surface thereby toremove a more or less stationary boundary layer which would otherwiseprevent an eiiective transfer of heat. Heating apparatus and heatexchangers of this character are disclosed and claimed in the copendingapplications of William C. Parrish, Serial Nos. 490,162, filed June 9,1943, now Patent No. 2,432,929, granted Dec. 16, 1947, and 494,155,filed July 10, 1943, now Patent No. 2,483,737, granted Oct. 29, 1949,while heat exchangers of the type including tapered conduits orpassageways for the hot products of combustion are disclosed and claimedin the copending application of Lynn A. Williams, Jr., Serial No.477,191, filed February 26, 1943, now Patent No. 2,457,513, granted Dec.28, 1948, all of which are assigned to the assignee of the presentapplication.

The construction of heat exchangers including spiral paths for one ofthe fluids has been difficult and heretofore has been done manually. Asa result they can be made but slowly and expensively.

The primary object of the present invention is the provision of a newand improved method of making heat exchangers, a new and improved heatexchanger, and new and improved apparatus for making the heat exchanger.

Another object of the present invention is the provision of a new andimproved method of making a heat exchanger which comprises the step ofexpanding a structure including a pair of wall defining portions intodesired shape by applying fluid pressure between the wall portions.

Another and more specific, object of the present invention is theprovision of a new and improved method of making heat exchangerscomprising the step of expanding a structure including a pair of walldefining portions by applying fluid pressure therebetween andrestricting the resulting expansion or deformation of the portions sothat they have a desired shape,

Another and more specific object of the present invention is theprovision of a new and improved method of making a heat exchanger, whichcomprises the steps set forth in the preceding paragraph and wherein thestructure is a double walled Another object of the present invention isto provide a new and improved heat exchanger which may be readilyfabricated by welding and the application of pressure.

A further object of the present invention is to provide a new andimproved apparatus for making heat exchangers of the type specifiedhereinabove which includes separable parts adapted to surround theheader and wrap assembly and to limit the deformation thereof underpressure so that the assembly will have the desired shape after theapplication of fluid pressure to expand the same.

Other objects and advantages of the present invention will become moreapparent from the ensuing description of the method of making the heatexchanger, the apparatus for making the heat exchanger, and the heatexchanger itself, in the course of which reference is had to theaccompanying drawings in which:

Fig. 1 is a fragmentary front elev-ational view,.

partly broken away, of apparatus for making the heat exchanger includinga source of fluid pressure and of a die for limiting the expansion of ofpressure therein to expand it into desired.

shape;

Fig. 3 is a view of the apparatus shown; inFig, 2 taken along the line3--3 of the latter figure;

Fig. 4 is an axial cross-sectionalview of 'the diei for limiting theexpansion of; the assembly-intodesired shape and after such expansionhas taken place, the view being taken along the broken line 44 of Fig.5a;

Figs. 5, 5a, and 5b are fragmentary transverse cross-sectional viewstaken along the lines 5-5, Sat-5a, and 522-52) of Fig. 4; Fig. 5illustrates thewrapand header assembly within the dieprior to theapplication of pressure therein; Fig. 5a illustrates the sameafter theapplication of pressure and the expansion of the walls into the shapedefined by the die; and Fig. 51) illustrates the assembly within the diebody but with an in portion of the die removed;

Fig.- 6 is a transverse cross-sectional view of the die taken along theline G -G ofFig. 4, with the wrap and header assembly omitted, it may beconsidered also to be an elevational view of one end assembly of thedie;

Fig. 7 is an axial cross-sectional view, on a reduced scale, of one formof heater with which the heat exchanger of the present invention may beutilized; and

Fig. 8 is a transverse cross-sectional View through the heater takenalong the line 8--8- of Fig. '7'.

Referring first to Fig. '7, it. may be noted that theheater which isindicated as a whole by refer ence character I0 is supplied withcombustible mixture by a carburetor !2- of any conventional or suitabletype. The carburetor receives fuel through a fuel supply line H-controlled by the usual, solenoid valve i5. Thecarburetor receivescombustion air from the heater through combustion air pipe 18' whichpasses into the heater through a tapered outlet end 20 ofthe heatercasing 22. This end of the combustion air pipe is so positioned thatpart of the heated air leaving the novel heat exchanger 24 of thepresent invention flows into this pipe and then to. the carburetor 12.The remainder of the heated air flows t0 the aircraft cabin or otherspace or spaces to be heated through a conduit 25.

g The combustible mixture of fuel and air formed by the carburetor I2 isconducted through a 00. duit 28 to the combustion chamber .30, theconduit passing through the heater casing 22 and wall 32 of thecombustion chamber. The delivery nd of the conduit 28, or induction pipeas it may be called, is curved as indicated by reference character 34and terminates in a straight outlet portion 36 coaxial with thecylindricalwall of the combustion chamber and directed toward adome-shaped inward projection 38 provided by the end wall 40 of thecombustion chamber. The combustible mixture supplied to the combustionchamber is initially ignited by an igniter 42.

The combustion chamber illustrated has numerous advantages as set forthin the previously referred to copending application of William C.Parrish, application Serial Number 494,155. Whirling vortices of burninggases are formed 4 within the combustion chamber from whence the hotproducts of combustion fiow to the heat exchanger 24.

Before describing the heat exchanger in detail, it may be noted that thecombustion chamber 30 is secured: to one end of the-heat exchangersubstantially coaxially; of the unit. More specifically, it is securedto a combustion end header 44, thev construction of which will bedescribed in greater detail hereinafter. The opposite end of the heatexchanger includes a header 4% closing that end. The combined combustionchamber and heat exchanger assembly is fioatingly secured within theheater casing 22 in a manner enabling the assembly to move relative tothe casing, thereby to avoid undue stresses and strains; resulting fromheating of the assembly during operation. The combustion chamber ismounted upon a bracket 48 secured to the inside of the heat exchangercasing. The opposite end is resiliently supported by a three-armedbracket 50-simi1ar-ly secured to the casing and slidably receiving a pin52 secured in suitable manner (as: by welding) to the header 4.5. Theheat. ex-

, changer I4 is resiliently held substantially cen..

trally of the heater casing by a plurality of circumferentially spacedclips or plates 54 (see Fig. 8).. changer in. the casing whilepermitting movement. thereof relative to the casing, which movement. mayresult from expansion and contraction of the heat exchanger due to thestarting. and stop.- ping of the heater. In effect, there is provided afloating mounting for the heat exchanger which provides for clockwiseand counter-clockwise ro.-. tation of the outer portion of the heatexchanger relative to the casing and which also permits the heatexchanger to. shift sidewise of the casing. The pin 52 permits axialexpansion and contrac-. tion ofthe heat exchanger.

The products of combustion are exhausted through a nipple 56 which issuitably secured as by welding to the heat exchanger unit and whichpasses through the heater casing 22. A suitable exhaust conduit 58 maybe secured to the nipple to lead the products of combustion to asuitable region.

The heat exchangerof the present invention is constructed essentially ofthe two previously re-. ferred to. headers 44 and 46 and a wrap 60 madefrom a single piece of sheet metal bent back upon itself in a manner nowabout to be described in detail, thereby to form a double walledstructure which is spiraled about the axis of the heater, the successivespirals being spaced from each other to form therebetween a pair ofpassageways 62- and 64, the first ofwhich is a spiral passageway leadingfrom the center of the heat exchanger unit to the exhaust nipple 55, andthe second-of which is an axial (and spiral) passageway extending fromend to end of the heat exchanger unit. Passagew-ay 62 is for a firstmedium, in this case the hot products of combustion, and the secondpassageway. 64 is for a second medium, in this case the air to beheated.

The heat exchanger 24 of the present invention providing the spiral andaxial passageways for the hot products of combustion and air to beheated, respectively, may be constructed both economically and simply bythe novel method of the present invention. In the description of thismethod and of the novel heat exchanger itself and of the novel apparatusfor making the heat exchanger, reference will now be had moreparticularly to Figs. 1 to 6, inclusive.

These clips serve to center the heat ex--.v

The heat exchanger is constructed from the previously referred to pairof headers 44 and 46 and the wrap 60, which may be made of relativelythin metal plate such as stainless steel. Referring now moreparticularly to Figs. 2 and 3, it may be noted that both of the headersare generally cup-shaped and are disposed with their open ends facing inthe same direction for the purpose of facilitating assembly of the wrapand header assembly. The header 44 includes inner and outer axial wallportions 66 and 68, of which the former is annular and of which thelatter is of somewhat difierent shape and larger than the former. Theend wall It! is indented somewhat and provided with a pair of apertures12. A pair of threaded bushings M are secured to the inside of the endwall H3 in alignment with the apertures 72 to receive suitable fittingsso that fluid may be introduced Within the assembly to expand it intodesired shape in manner to be described shortly. The end wall and aportion of the axial wall 66 are cut away after the heat exchanger hasbeen formed in order that the combustion chamber 30 may be securedthereto in the manner illustrated in Fig. 7.

The other header 46 is of simpler shape having only an end wall 16 andan axial wall '18.

In order to give a suitable shape to the inner end of the passageway 62for the hot products of combustion, the axial walls 68 and T8 of theheaders are curved spirally for a portion of their peripheries asindicated by reference character 80 (see Fig. 3).

After the headers have been constructed, the wrap 60, which consists ofa suitable length of stainless steel plate, is curved around and securedto the headers as best illustrated in Fig. 3. From this figure it may benoted that the wrap 69 has its central portion encircling closely theheaders, and that the outer portions are substantially in abuttingrelation to each other as indicated by the reference characters 68A and603 indicating the opposite end portions of the wrap.

The assembly is united and sealed in suitable manner as by seam weldingwherever possible and by torch welding where seam welding cannot beused, as at the point 82 where the wrap portions 60A and 60B converge.Header 44 is first welded to the wrap through the opening provided byheader 46. Then header 46 is inserted and welded to the other edge ofthe wrap, following which the side and end edges of the wrap portions68A and 60B are welded together.

The wrap and header assembly, which is now in the form illustrated inFigs. 2 and 3, is then formed spirally, i. e., the portions 68A and 60Bof the wrap are curved spirally around the central portion including theheaders. In this stage of manufacture the assembly has the formillustrated in Fig. 5, where the assembly is illustrated in a formingdie.

After the assembly has been formed spirally, it is inserted into amulti-part, separable forming die, indicated generally by the referencecharacter 84, so that the sealed assembly may be expanded into desiredshape by the application of pressure therein. It is preferred that thepressure be fluid pressure, such as oil supplied by a high pressure pumpwhich will be described hereinafter.

The forming die 84 includes'a pair of end assemblies adapted to receivethe opposite ends of 3 the spiral header and wrap assembly, an external'die body adapted completely to surround the outside of the assembly,and a spiral passage spacer located centrally of the die and definingpassages adapted to receive the assembly. The interior of the die bodyand the spacer are shaped to conform to the shape desired to be given tothe heat exchanger. Preferably, the spacer is shaped to conform to theaxial air passages so that the space between portions of the spacer andbetween the spacer and the inner surface of the die body are of a shapecorresponding to the shape desired to be given to the spiral passagewayfor the hot products of combustion.

Referring now more particularly to Figs. 4 to 6, inclusive, andparticularly to Fig. 4, it may be seen that the die i i includes thespaced apart end assemblies 86 and 88, a central generally annular diebody 96, and the central inner air passage spacer 92. The annular diebody 90 may be made of a single piece of metal and it is provided at itsends with a plurality of circumferentially spaced apart threadedopenings 94 adapted to receive bolts for securing the main components ofthe forming die. Accurate positioning is provided by the diametricallyopposite pins 97 (Fig. 6).

The end assembly 86 includes a relatively thick end plate 98, which isprovided with a pair of apertures 99 for the purpose of receivingcoupling conduits Hi0 adapted to be threaded into the bushings W. Theend assembly also includes a number of parts which, when assembledtogether, are adapted to receive the combustion end header and thecombustion end of the header and wrap assembly. These parts include acentral circular plate 62 seated within a central recess in end plate $8and secured thereto by the countersunk screws HM. An annular plate !66is located next to the end plate and it has a central circular aperturefor receiving the axial the outer portion of retainer ring H2 and has aconfiguration corresponding to the cross section desired to be given tothe passageway 52 for the hot products of combustion. The retainer ringI #2 is provided with a spiral slot M6 to receive the end of the spacer92. The retainer rings H2 and H4 are secured to plate I06 by screws E26,and better positioning is provided by a plurality of pins 522 extendingthrough the plate M6, the retainer ring H2, and into retainer ring l M.

The end assembly 88 is constructed like the assembly 86, except that itfaces in the opposite direction, and the central circular plate 12s isshaped to receive the header 45, which, it may be remembered, has asomewhat simpler configuration than the header ti. Accordingly, theplate EM may be utilized to perform a function performed by a portion ofthe retainer ring H2.

In addition, a plate I25 corresponding to plate 106 is not apertured,and screws 528 are utilized .to secure the latter plate and. plate 1 tothe end plate corresponding to plate $8. the similarities inconstruction, it is believed In view of that a further description ofend assembly 88 is not required.

The spacer 92 is generally spiral in shape, and

ture dimensioned to fit between adjacent turns of the spirally curvedwrap with clearance, and applying fluid pressure within said structureto expand the bilaminar portion of the assembly against the spiral diestructure to the extent of said clearance, removing the heat exchangerfrom the die structure, and cutting away a portion of one header toprovide means for securing a combustion chamber to the heat exchanger.

3. A die for expanding into desired shape a spiral heat exchanger havinga spiral portion with Welded edge portions, including in combination,end portions adapted to abut against and hold the welded edge portionsof the unit, a separable interposed outer portion adapted to be securedbetween the end portions, and an interposed generally slpiral innerportion adapted to be secured between the end portions and to said outerportion, the spiral die portion having a space to receive the spiralportion of the unit and to limit the expansion thereof into desiredshape, and said interposed portions also having means for clamping theouter end of the spiral portion of said heat exchanger within said die,together with means for introducing fluid under pressure into the heatexchanger for expanding it within the die.

ARTHUR R. COLLINS.

JOHN H. LESLIE, II.

CHARLES T. NOVAK.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 701,549 Deering June 3, 1902705,614 Rogers July 29, 1902 1,111,198 Wacker Sept. 22, 1914 1,174,876Leiman Mar. 7, 1916 1,560,719 Olson Nov. 10, 1925 1,685,388 White Sept.25, 1928 1,709,865 Mufiiy Apr. 23, 1929 1,766,585 Banfield June 24, 19301,930,879 Linderoth Oct. 17, 1933 2,129,300 Bichowsky Sept. 6, 19382,193,345 Rosenblad Mar. 12, 1940 2,281,299 Steenstrup Apr. 28, 19422,306,526 Dalzell Dec. 29, 1942 FOREIGN PATENTS Number Country Date94,212 Switzerland Jan. 13, 1939

